Magnetic Memory Element Incorporating Dual Perpendicular Enhancement Layers

ABSTRACT

The present invention is directed to a magnetic memory element including a magnetic free layer structure incorporating two magnetic free layers separated by a perpendicular enhancement layer (PEL) and having a variable magnetization direction substantially perpendicular to layer planes thereof; an insulating tunnel junction layer formed adjacent to the magnetic free layer structure; a magnetic reference layer structure formed adjacent to the insulating tunnel junction layer opposite the magnetic free layer structure; an anti-ferromagnetic coupling layer formed adjacent to the magnetic reference layer structure; and a magnetic fixed layer formed adjacent to the anti-ferromagnetic coupling layer. The magnetic reference layer structure includes first, second, and third magnetic reference layers separated by two PELs and having a first invariable magnetization direction substantially perpendicular to layer planes thereof. The magnetic fixed layer has a second invariable magnetization direction substantially opposite to the first invariable magnetization direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.17/156,562, filed on Jan. 23, 2021, which is a continuation-in-part ofapplication Ser. No. 16/831,519, filed on Mar. 26, 2020, now U. S. Pat.No. 10,910,555, which is a continuation-in-part of application Ser. No.16/112,323, filed on Aug. 24, 2018, now U.S. Pat. No. 10,727,400, whichis a continuation of application Ser. No. 15/794,983, filed on Oct. 26,2017, now U.S. Pat. No. 10,079,388, which is a continuation ofapplication Ser. No. 14/797,458, filed on Jul. 13, 2015, now U.S. Pat.No. 9,831,421, which is a continuation-in-part of application Ser. No.14/560,740, filed on Dec. 4, 2014, now U.S. Pat. No. 9,082,951, which isa continuation-in-part of application Ser. No. 14/256,192, filed on Apr.18, 2014, now U.S. Pat. No. 9,647,202, which is a continuation-in-partof application Ser. No. 14/053,231, filed on Oct. 14, 2013, now U.S.Pat. No. 9,070,855, which is a continuation-in-part of application Ser.No. 14/026,163, filed on Sep. 13, 2013, now U.S. Pat. No. 9,024,398,which is a continuation-in-part of application Ser. No. 13/029,054,filed on Feb. 16, 2011, now U.S. Pat. No. 8,598,576, and acontinuation-in-part of application Ser. No. 13/277,187, filed on Oct.19, 2011, now abandoned, which claims priority to provisionalapplication No. 61/483,314, filed on May 6, 2011 and is acontinuation-in-part of application Ser. No. 12/965,733, filed on Dec.10, 2010, now U.S. Pat. No. 8,623,452. The application Ser. No.14/797,458 is also a continuation-in-part of application Ser. No.14/657,608, filed on Mar. 13, 2015, now U.S. Pat. No. 9,318,179, whichis a continuation of application Ser. No. 13/225,338, filed on Sep. 2,2011, now U.S. Pat. No. 9,019,758, which claims priority to provisionalapplication No. 61/382,815, filed on Sep. 14, 2010. All of theseapplications are incorporated herein by reference in their entirety,including their specifications.

BACKGROUND

The present invention relates to a magnetic random access memory (MRAM)device, and more particularly, to a spin transfer torque MRAM deviceincluding at least a perpendicular enhancement layer in its memoryelement.

Spin transfer torque magnetic random access memory (STT-MRAM) is a newclass of non-volatile memory, which can retain the stored informationwhen powered off. An STT-MRAM device normally comprises an array ofmemory cells, each of which includes at least a magnetic memory elementand a selection element coupled in series between appropriateelectrodes. Upon application of an appropriate voltage or current to themagnetic memory element, the electrical resistance of the magneticmemory element would change accordingly, thereby switching the storedlogic in the respective memory cell.

FIG. 1 is a schematic circuit diagram of a conventional STT-MRAM device30, which comprises a plurality of memory cells 32, each of the memorycells 32 including a selection transistor 34 coupled to a magneticmemory element 36; a plurality of parallel word lines 38 with each beingcoupled to the gates of a respective row of the selection transistors 34in a first direction; and a plurality of parallel bit lines 40 with eachbeing coupled to a respective row of the memory elements 36 in a seconddirection perpendicular to the first direction; and optionally aplurality of parallel source lines 42 with each being coupled to arespective row of the selection transistors 34 in the first or seconddirection.

FIG. 2 shows a conventional magnetic memory element comprising amagnetic reference layer 50 and a magnetic free layer 52 with aninsulating tunnel junction layer 54 interposed therebetween, therebycollectively forming a magnetic tunneling junction (MTJ) 56. Themagnetic reference layer 50 and free layer 52 have magnetizationdirections 58 and 60, respectively, which are substantiallyperpendicular to the respective layer planes. Therefore, the MTJ 56 is aperpendicular type comprising the magnetic layers 50 and 52 withperpendicular anisotropy. Upon application of an appropriate currentthrough the perpendicular MTJ 56, the magnetization direction 60 of themagnetic free layer 52 can be switched between two directions: paralleland anti-parallel with respect to the magnetization direction 58 of themagnetic reference layer 50. The insulating tunnel junction layer 54 isnormally made of a dielectric material with a thickness ranging from afew to a few tens of angstroms. However, when the magnetizationdirections 60 and 58 of the magnetic free layer 52 and reference layer50 are substantially parallel, electrons polarized by the magneticreference layer 50 may tunnel through the insulating tunnel junctionlayer 54, thereby decreasing the electrical resistivity of theperpendicular MTJ 56. Conversely, the electrical resistivity of theperpendicular MTJ 56 is high when the magnetization directions 58 and 60of the magnetic reference layer 50 and free layer 52 are substantiallyanti-parallel. Accordingly, the stored logic in the magnetic memoryelement can be switched by changing the magnetization direction 60 ofthe magnetic free layer 52.

One of many advantages of STT-MRAM over other types of non-volatilememories is scalability. As the size of the perpendicular MTJ 56 isreduced, the current required to switch the magnetization direction 60of the magnetic free layer 52 is reduced accordingly, thereby reducingpower consumption. However, the thermal stability of the magnetic layers50 and 52, which is required for long term data retention, also degradeswith miniaturization of the perpendicular MTJ 56.

For the foregoing reasons, there is a need for an STT-MRAM device thathas a thermally stable perpendicular MTJ memory element and that can beinexpensively manufactured.

SUMMARY

The present invention is directed to a spin transfer torque (STT)magnetic random access memory (MRAM) element that satisfies this need.An STT-MRAM element having features of the present invention includes amagnetic tunnel junction (MTJ) structure formed between an optional seedlayer and an optional cap layer. The MTJ structure comprises a magneticfree layer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween, and a magneticfixed layer separated from the magnetic reference layer structure by ananti-ferromagnetic coupling layer. The magnetic free layer structureincludes one or more magnetic free layers having a variablemagnetization direction substantially perpendicular to layer planesthereof. The one or more magnetic free layers comprise cobalt and iron.The magnetic reference layer structure includes first and secondmagnetic reference layers having a first invariable magnetizationdirection substantially perpendicular to layer planes thereof, and aperpendicular enhancement layer (PEL) interposed between the first andsecond magnetic reference layers. The first magnetic reference layer isformed adjacent to the insulating tunnel junction layer and comprisescobalt, iron, and boron. The PEL comprises one of molybdenum, tungsten,magnesium, or tantalum. The magnetic fixed layer includes one or moremagnetic sublayers having a second invariable magnetization directionthat is substantially perpendicular to layer planes thereof and issubstantially opposite to the first invariable magnetization direction.

According to another aspect of the present invention, an MTJ structurecomprises a magnetic free layer structure and a magnetic reference layerstructure with an insulating tunnel junction layer interposedtherebetween, and a magnetic fixed layer separated from the magneticreference layer structure by an anti-ferromagnetic coupling layer. Themagnetic free layer structure includes first and second magnetic freelayers having a variable magnetization direction substantiallyperpendicular to layer planes thereof, and a first perpendicularenhancement layer (PEL) interposed between the first and second magneticfree layers. The first and second magnetic free layers comprise cobalt,iron, and boron. The first PEL comprises one of magnesium, magnesiumoxide, molybdenum, tungsten, or tantalum. The magnetic reference layerstructure includes first and second magnetic reference layers having afirst invariable magnetization direction substantially perpendicular tolayer planes thereof, and a second PEL interposed between the first andsecond magnetic reference layers. The first magnetic reference layer isformed adjacent to the insulating tunnel junction layer and comprisescobalt, iron, and boron. The second PEL comprises one of molybdenum,tungsten, magnesium, or tantalum. The magnetic fixed has a secondinvariable magnetization direction that is substantially perpendicularto a layer plane thereof and is substantially opposite to the firstinvariable magnetization direction.

According to still another aspect of the present invention, an MTJstructure comprises a magnetic free layer structure and a magneticreference layer structure with an insulating tunnel junction layerinterposed therebetween, and a magnetic fixed layer separated from themagnetic reference layer structure by an anti-ferromagnetic couplinglayer. The magnetic free layer structure includes first, second, andthird magnetic free layers having a variable magnetization directionsubstantially perpendicular to layer planes thereof, a firstperpendicular enhancement layer (PEL) interposed between the first andsecond magnetic free layers, and a second PEL interposed between thesecond and third magnetic free layers. The first, second, and thirdmagnetic free layers comprise cobalt, iron, and boron. The first andsecond PELs each independently comprise one of magnesium, magnesiumoxide, molybdenum, tungsten, or tantalum, titanium, zirconium, vanadium,aluminum, beryllium, or barium. The magnetic reference layer structureincludes first and second magnetic reference layers having a firstinvariable magnetization direction substantially perpendicular to layerplanes thereof, and a third PEL interposed between the first and secondmagnetic reference layers. The first magnetic reference layer is formedadjacent to the insulating tunnel junction layer and comprises cobalt,iron, and boron. The third PEL comprises one of molybdenum, tungsten,magnesium, or tantalum. The magnetic fixed has a second invariablemagnetization direction that is substantially perpendicular to a layerplane thereof and is substantially opposite to the first invariablemagnetization direction.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a schematic circuit diagram of a conventional STT-MRAM device;

FIG. 2 is a cross-sectional view of a conventional magnetic memoryelement comprising a perpendicular magnetic tunnel junction (MTJ);

FIGS. 3A and 3B are cross-sectional views of a first embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 4A and 4B are cross-sectional views of a second embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 5A and 5B are cross-sectional views of a third embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 6A and 6B are cross-sectional views of a fourth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 7A and 7B are cross-sectional views of a fifth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 8A and 8B are cross-sectional views of a sixth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 9A and 9B are cross-sectional views of a seventh embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 10A and 10B are cross-sectional views of an eighth embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 11A and 11B are cross-sectional views of a ninth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 12A and 12B are cross-sectional views of a tenth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 13A and 13B are cross-sectional views of an eleventh embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 14A and 14B are cross-sectional views of a twelfth embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 15A and 15B are cross-sectional views of exemplary MTJ structurescorresponding to the fifth embodiment of the present invention;

FIGS. 16A and 16B are cross-sectional views of exemplary magnetic freelayer structures corresponding to various embodiments of the presentinvention;

FIGS. 17A and 17B are cross-sectional views of exemplary magneticreference layer structures corresponding to various embodiments of thepresent invention;

FIGS. 18A and 18B are cross-sectional views of exemplary structures thatinclude magnetic reference layer structure and magnetic fixed layer inaccordance with various embodiments of the present invention;

FIGS. 19A and 19B are cross-sectional views of the exemplary MTJstructures in which the magnetic reference layer structure includes thefirst and second magnetic reference layers without a perpendicularenhancement layer interposed therebetween;

FIGS. 20A and 20B are cross-sectional views of a thirteenth embodimentof the present invention as applied to a perpendicular MTJ memoryelement;

FIGS. 21A and 21B are cross-sectional views of exemplary magnetic freelayer structures that include two perpendicular enhancement layers;

FIGS. 22A and 22B are cross-sectional views of exemplary magnetic freelayer structures that include three perpendicular enhancement layers;

FIGS. 23A and 23B are cross-sectional views of the fourth embodiment ofthe present invention that incorporates the magnetic free layerstructure including two perpendicular enhancement layers;

FIGS. 24A and 24B are cross-sectional views of exemplary magneticreference layer structures that include two perpendicular enhancementlayers; and

FIGS. 25A and 25B are cross-sectional views of exemplary magneticreference layer structures that include three perpendicular enhancementlayers.

For purposes of clarity and brevity, like elements and components willbear the same designations and numbering throughout the Figures, whichare not necessarily drawn to scale.

DETAILED DESCRIPTION

In the Summary above and in the Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures of the invention. It is to be understood that the disclosure ofthe invention in this specification includes all possible combinationsof such particular features. For example, where a particular feature isdisclosed in the context of a particular aspect or embodiment of theinvention, or a particular claim, that feature can also be used, to theextent possible, in combination with and/or in the context of otherparticular aspects and embodiments of the invention, and in theinvention generally.

Where reference is made herein to a material AB composed of element Aand element B, the material AB may be an alloy, a compound, or acombination thereof, unless otherwise specified or the context excludesthat possibility.

Where reference is made herein to a multilayer structure [C/D] formed byinterleaving layer(s) of material C with layer(s) of material D, atleast one of material C and material D may be made of elemental metal,elemental non-metal, alloy, or compound. The multilayer structure [C/D]may contain any number of layers but may have as few as two layersconsisting of one layer of material C and one layer of material D. Themultilayer structure [C/D] has a stack structure that may begin with onematerial and end with the other material such as C/D/C/D or may beginwith one material and end with the same material such as C/D/C.Individual layers of material C may or may not have the same thickness.Likewise, individual layers of material D may or may not have the samethickness. The multilayer structure [C/D] may or may not exhibit thecharacteristic satellite peaks associated with superlattice whenanalyzed by X-ray or neutron diffraction.

The term “noncrystalline” means an amorphous state or a state in whichfine crystals are dispersed in an amorphous matrix, not a single crystalor polycrystalline state. In case of state in which fine crystals aredispersed in an amorphous matrix, those in which a crystalline peak issubstantially not observed by, for example, X-ray diffraction can bedesignated as “noncrystalline.”

The term “magnetic dead layer” means a layer of supposedly ferromagneticmaterial that does not exhibit a net magnetic moment in the absence ofan external magnetic field. A magnetic dead layer of several atomiclayers may form in a magnetic film in contact with another layermaterial owing to intermixing of atoms at the interface. Alternatively,a magnetic dead layer may form as thickness of a magnetic film decreasesto a point that the magnetic film becomes superparamagnetic.

As understood by those skilled in the art, many magnetic films commonlyused in magnetic random access memory (MRAM) elements, such as but notlimited to Fe, CoFe, and CoFeB that have a body-centered cubic (BCC)lattice structure, have in-plane magnetization (magnetization directionbeing parallel to the film plane) because of shape anisotropy. However,it is desirable to change the magnetization of magnetic films in theMRAM element from in-plane to perpendicular orientation because ofimprovement in thermal stability. The present invention is directed to aspin transfer torque magnetic random access memory (STTMRAM) elementutilizing perpendicular enhancement layers (PELs) to verticalize themagnetization of a magnetic free layer and/or a magnetic referencelayer, which may otherwise have in-plane magnetization.

A first embodiment of the present invention as applied to aperpendicular MTJ memory element that includes at least a perpendicularenhancement layer (PEL) to improve the perpendicular anisotropy ofmagnetic layers adjacent thereto will now be described with reference toFIG. 3A. Referring now to FIG. 3A, the illustrated memory element 114includes a magnetic tunnel junction (MTJ) structure 116 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure116 comprises a magnetic free layer structure 122 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween. The magnetic reference layer structure 124and the magnetic free layer structure 122 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first invariable magnetization direction 125 substantiallyperpendicular to the layer planes thereof. The first magnetic referencelayer 134 may comprise one or more magnetic sublayers having the firstinvariable magnetization direction 125. Similarly, the second magneticreference layer 136 may comprise one or more magnetic sublayers havingthe first invariable magnetization direction 125.

The stacking order of the individual layers in the MTJ structure 116 ofthe memory element 114 may be inverted as illustrated in FIG. 3B. Thememory element 114′ of FIG. 3B has an MTJ structure 116′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 116. Accordingly, the magnetic free layer structure 122 andthe magnetic reference layer structure 124 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively.

A second embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 4A. The memory element 140 includes amagnetic tunnel junction (MTJ) structure 142 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 142 comprisesa magnetic free layer structure 122 and a magnetic reference layer 144with an insulating tunnel junction layer 126 interposed therebetween.The magnetic reference layer 144 and the magnetic free layer structure122 may be formed adjacent to the optional seed layer 118 and cap layer120, respectively.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first invariable magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first invariable magnetization direction 145.

The stacking order of the individual layers in the MTJ structure 142 ofthe memory element 140 may be inverted as illustrated in FIG. 4B. Thememory element 140′ of FIG. 4B has an MTJ structure 142′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 142. Accordingly, the magnetic free layer structure 122 andthe magnetic reference layer 144 may be formed adjacent to the optionalseed layer 118 and cap layer 120, respectively.

A third embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 5A. The memory element 150 includes amagnetic tunnel junction (MTJ) structure 152 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 152 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween.The magnetic reference layer structure 124 and the magnetic free layer154 may be formed adjacent to the optional seed layer 118 and cap layer120, respectively.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst invariable magnetization direction 125 substantially perpendicularto the layer planes thereof. The first magnetic reference layer 134 maycomprise one or more magnetic sublayers having the first invariablemagnetization direction 125. Similarly, the second magnetic referencelayer 136 may comprise one or more magnetic sublayers having the firstinvariable magnetization direction 125.

The stacking order of the individual layers in the MTJ structure 152 ofthe memory element 150 may be inverted as illustrated in FIG. 5B. Thememory element 150′ of FIG. 5B has an MTJ structure 152′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 152. Accordingly, the magnetic free layer 154 and the magneticreference layer structure 124 may be formed adjacent to the optionalseed layer 118 and cap layer 120, respectively.

The optional seed layer 118 of the memory elements 114, 114′, 140, 140′,150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, mayfacilitate the optimal growth of magnetic layers formed thereon toincrease perpendicular anisotropy. The seed layer 118 may also serve asa bottom electrode to the MTJ structures 116, 116′, 142, 142′, 152, and152′. The seed layer 118 may comprise one or more seed sublayers, whichmay be formed adjacent to each other.

The optional cap layer 120 of the memory elements 114, 114′, 140, 140′,150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, mayfunction as a top electrode for the MTJ structures 116, 116′, 142, 142′,152, and 152′ and may also improve the perpendicular anisotropy of themagnetic layer formed adjacent thereto during annealing. The cap layer120 may comprise one or more cap sublayers, which may be formed adjacentto each other.

For the MTJ structures 116, 116′, 142, 142′, 152, and 152′ of FIGS. 3A,3B, 4A, 4B, 5A, and 5B, the magnetic free layer structure 122 and themagnetic reference layer structure 124 include therein the perpendicularenhancement layers 132 and 138, respectively. The perpendicularenhancement layers 132 and 138 may further improve the perpendicularanisotropy of the magnetic layers formed adjacent thereto duringdeposition or annealing or both. Each of the perpendicular enhancementlayers 132 and 138 may have a single layer structure or may comprisemultiple perpendicular enhancement sublayers, which may be formedadjacent to each other.

A fourth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 6A. The memory element 160 includes amagnetic tunnel junction (MTJ) structure 162 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 162 comprisesa magnetic free layer structure 122 and a magnetic reference layerstructure 124 with an insulating tunnel junction layer 126 interposedtherebetween, an anti-ferromagnetic coupling layer 164 formed adjacentto the magnetic reference layer structure 124, and a magnetic fixedlayer 166 formed adjacent to the anti-ferromagnetic coupling layer 164.The magnetic fixed layer 166 and the magnetic free layer structure 122may be formed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 160 of FIG. 6A is different from thememory element 114 of FIG. 3A in that the anti-ferromagnetic couplinglayer 164 and the magnetic fixed layer 166 have been inserted in betweenthe optional seed layer 118 and the magnetic reference layer structure124.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first invariable magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first invariablemagnetization direction 125.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 162 ofthe memory element 160 may be inverted as illustrated in FIG. 6B. Thememory element 160′ of FIG. 6B has an MTJ structure 162′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 162. Accordingly, the magnetic free layer structure 122 andthe magnetic fixed layer 166 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

A fifth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 7A. The memory element 170 includes amagnetic tunnel junction (MTJ) structure 172 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 172 comprisesa magnetic free layer structure 122 and a magnetic reference layer 144with an insulating tunnel junction layer 126 interposed therebetween, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer 144, and a magnetic fixed layer 166 formed adjacent tothe anti-ferromagnetic coupling layer 164. The magnetic fixed layer 166and the magnetic free layer structure 122 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively. The memoryelement 170 of FIG. 7A is different from the memory element 140 of FIG.4A in that the anti-ferromagnetic coupling layer 164 and the magneticfixed layer 166 have been inserted in between the optional seed layer118 and the magnetic reference layer 144.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first invariable magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first invariable magnetization direction 145.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 145. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 172 ofthe memory element 170 may be inverted as illustrated in FIG. 7B. Thememory element 170′ of FIG. 7B has an MTJ structure 172′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 172. Accordingly, the magnetic free layer structure 122 andthe magnetic fixed layer 166 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

A sixth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 8A. The memory element 180 includes amagnetic tunnel junction (MTJ) structure 182 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 182 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer structure 124, and a magnetic fixed layer 166 formedadjacent to the anti-ferromagnetic coupling layer 164. The magneticfixed layer 166 and the magnetic free layer 154 may be formed adjacentto the optional seed layer 118 and cap layer 120, respectively. Thememory element 180 of FIG. 8A is different from the memory element 150of FIG. 5A in that the anti-ferromagnetic coupling layer 164 and themagnetic fixed layer 166 have been inserted in between the optional seedlayer 118 and the magnetic reference layer structure 124.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst invariable magnetization direction 125 substantially perpendicularto the layer planes thereof. Each of the first magnetic reference layer134 and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first invariable magnetization direction125.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 182 ofthe memory element 180 may be inverted as illustrated in FIG. 8B. Thememory element 180′ of FIG. 8B has an MTJ structure 182′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 182. Accordingly, the magnetic free layer 154 and the magneticfixed layer 166 may be formed adjacent to the optional seed layer 118and cap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 162,162′, 172, 172′, 182, and 182′ of FIGS. 6A, 6B, 7A, 7B, 8A, and 8B,respectively, have the magnetic fixed layer 166 anti-ferromagneticallycoupled to the magnetic reference layer structure 124 or the magneticreference layer 144 through the anti-ferromagnetic coupling layer 164.The magnetic fixed layer 166 is not an “active” layer like the magneticreference layer structure and the magnetic free layer structure, whichalong with the tunnel junction layer 126 collectively form an MTJ thatchanges resistivity when a spin-polarized current pass therethrough. Themagnetic fixed layer 166, which has an opposite magnetization directioncompared with the magnetic reference layer structure 124 and themagnetic reference layer 144, may pin or stabilize the magnetization ofthe magnetic reference layer structure 124 and the magnetic referencelayer 144 and may cancel, as much as possible, the external magneticfield exerted by the magnetic reference layer structure 124 or themagnetic reference layer 144 on the magnetic free layer structure 122 orthe magnetic free layer 154, thereby minimizing the offset field or netexternal field in the magnetic free layer structure 122 or the magneticfree layer 154.

A seventh embodiment of the present invention as applied to an MTJmemory element is illustrated in FIG. 9A. The memory element 190includes a magnetic tunnel junction (MTJ) structure 192 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure192 comprises a magnetic free layer structure 122 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122, and a magnetic compensation layer 196formed adjacent to the tuning layer 194. The magnetic reference layerstructure 124 and the magnetic compensation layer 196 may be formedadjacent to the optional seed layer 118 and cap layer 120, respectively.The memory element 190 of FIG. 9A is different from the memory element114 of FIG. 3A in that the tuning layer 194 and the magneticcompensation layer 196 have been inserted in between the magnetic freelayer structure 122 and the optional cap layer 120.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first invariable magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first invariablemagnetization direction 125.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The stacking order of the individual layers in the MTJ structure 192 ofthe memory element 190 may be inverted as illustrated in FIG. 9B. Thememory element 190′ of FIG. 9B has an MTJ structure 192′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 192. Accordingly, the magnetic compensation layer 196 and themagnetic reference layer structure 124 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively.

An eighth embodiment of the present invention as applied to an MTJmemory element is illustrated in FIG. 10A. The memory element 200includes a magnetic tunnel junction (MTJ) structure 202 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure202 comprises a magnetic free layer structure 122 and a magneticreference layer 144 with an insulating tunnel junction layer 126interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122, and a magnetic compensation layer 196formed adjacent to the tuning layer 194. The magnetic reference layer144 and the magnetic compensation layer 196 may be formed adjacent tothe optional seed layer 118 and cap layer 120, respectively. The memoryelement 200 of FIG. 10A is different from the memory element 140 of FIG.4A in that the tuning layer 194 and the magnetic compensation layer 196have been inserted in between the magnetic free layer structure 122 andthe optional cap layer 120.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first invariable magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first invariable magnetization direction 145.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 145. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The stacking order of the individual layers in the MTJ structure 202 ofthe memory element 200 may be inverted as illustrated in FIG. 10B. Thememory element 200′ of FIG. 10B has an MTJ structure 202′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 202. Accordingly, the magnetic compensation layer 196 and themagnetic reference layer 144 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

A ninth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 11A. The memory element 210 includes amagnetic tunnel junction (MTJ) structure 212 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 212 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween, atuning layer 194 formed adjacent to the magnetic free layer 154, and amagnetic compensation layer 196 formed adjacent to the tuning layer 194.The magnetic reference layer structure 124 and the magnetic compensationlayer 196 may be formed adjacent to the optional seed layer 118 and caplayer 120, respectively. The memory element 210 of FIG. 11A is differentfrom the memory element 150 of FIG. 5A in that the tuning layer 194 andthe magnetic compensation layer 196 have been inserted in between themagnetic free layer 154 and the optional cap layer 120.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst invariable magnetization direction 125 substantially perpendicularto the layer planes thereof. Each of the first magnetic reference layer134 and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first invariable magnetization direction125.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The stacking order of the individual layers in the MTJ structure 212 ofthe memory element 210 may be inverted as illustrated in FIG. 11B. Thememory element 210′ of FIG. 11B has an MTJ structure 212′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 212. Accordingly, the magnetic compensation layer 196 and themagnetic reference layer structure 124 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3AB-5A/B, respectively, the MTJ structures 192, 192′, 202, 202′,212, and 212′ of FIGS. 9A/B-11A/B, respectively, have the magneticcompensation layer 196 separated from the magnetic free layer structure122 or the magnetic free layer 154 by the tuning layer 194. Similar tothe magnetic fixed layer 166, the magnetic compensation layer 196 is notan “active” layer like the magnetic reference layer structure 124 andthe magnetic free layer structure 122, which along with the tunneljunction layer 126 collectively form an MTJ that changes resistivitywhen a spin-polarized current pass therethrough. One of the functions ofthe magnetic compensation layer 196, which has an opposite magnetizationdirection compared with the magnetic reference layer structure 124 andthe magnetic reference layer 144, is to cancel, as much as possible, theexternal magnetic field exerted by the magnetic reference layerstructure 124 or the magnetic reference layer 144 on the magnetic freelayer structures 122 or the magnetic free layer 154, thereby minimizingthe offset field or net external field in the magnetic free layerstructures 122 or the magnetic free layer 154. The strength of theexternal magnetic field exerted by the magnetic compensation layer 196on the magnetic free layer structure 122 or the magnetic free layer 154can be modulated by varying the thickness of the tuning layer 194, whichchanges the separation distance between the magnetic compensation layer196 and the magnetic free layer structure 122 or the magnetic free layer154.

The tuning layer 194 may also improve the perpendicular anisotropy ofthe magnetic layers formed adjacent thereto. The tuning layer 194 maycomprise one or more tuning sublayers, which may be formed adjacent toeach other.

A tenth embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 12A. The memoryelement 220 includes a magnetic tunnel junction (MTJ) structure 222 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 222 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a tuning layer 194 formedadjacent to the magnetic free layer structure 122 opposite theinsulating tunnel junction layer 126, a magnetic compensation layer 196formed adjacent to the tuning layer 194 opposite the magnetic free layerstructure 122, an anti-ferromagnetic coupling layer 164 formed adjacentto the magnetic reference layer structure 124 opposite the insulatingtunnel junction layer 126, and a magnetic fixed layer 166 formedadjacent to the anti-ferromagnetic coupling layer 164 opposite themagnetic reference layer structure 124. The magnetic fixed layer 166 andthe magnetic compensation layer 196 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively. The memoryelement 220 of FIG. 12A is different from the memory element 190 of FIG.9A in that the magnetic fixed layer 166 and the anti-ferromagneticcoupling layer 164 have been inserted in between the magnetic referencelayer structure 124 and the optional seed layer 118.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first invariable magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first invariablemagnetization direction 125.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 222 ofthe memory element 220 may be inverted as illustrated in FIG. 12B. Thememory element 220′ of FIG. 12B has an MTJ structure 222′ that has thesame layers but with the inverted stacking order comparing with the MTJstructure 222. Accordingly, the magnetic compensation layer 196 and themagnetic fixed layer 166 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

An eleventh embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 13A. The memoryelement 224 includes a magnetic tunnel junction (MTJ) structure 226 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 226 comprises a magnetic free layer structure 122 and amagnetic reference layer 144 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122 opposite the insulating tunneljunction layer 126, a magnetic compensation layer 196 formed adjacent tothe tuning layer 194 opposite the magnetic free layer structure 122, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer 144 opposite the insulating tunnel junction layer 126,and a magnetic fixed layer 166 formed adjacent to the anti-ferromagneticcoupling layer 164 opposite the magnetic reference layer 144. Themagnetic fixed layer 166 and the magnetic compensation layer 196 may beformed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 224 of FIG. 13A is different from thememory element 200 of FIG. 10A in that the magnetic fixed layer 166 andthe anti-ferromagnetic coupling layer 164 have been inserted in betweenthe magnetic reference layer 144 and the optional seed layer 118.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first invariable magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first invariable magnetization direction 145.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 145. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 145. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 226 ofthe memory element 224 may be inverted as illustrated in FIG. 13B. Thememory element 224′ of FIG. 13B has an MTJ structure 226′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 226. Accordingly, the magnetic compensation layer 196 and themagnetic fixed layer 166 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

A twelfth embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 14A. The memoryelement 228 includes a magnetic tunnel junction (MTJ) structure 229 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 229 comprises a magnetic free layer 154 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer 154 opposite the insulating tunnel junction layer126, a magnetic compensation layer 196 formed adjacent to the tuninglayer 194 opposite the magnetic free layer 154, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124 opposite the insulating tunnel junction layer 126, and amagnetic fixed layer 166 formed adjacent to the anti-ferromagneticcoupling layer 164 opposite the magnetic reference layer structure 124.The magnetic fixed layer 166 and the magnetic compensation layer 196 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 228 of FIG. 14A is different from thememory element 210 of FIG. 11A in that the magnetic fixed layer 166 andthe anti-ferromagnetic coupling layer 164 have been inserted in betweenthe magnetic reference layer structure 124 and the optional seed layer118.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst invariable magnetization direction 125 substantially perpendicularto the layer planes thereof. Each of the first magnetic reference layer134 and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first invariable magnetization direction125.

The magnetic compensation layer 196 has a third invariable magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic compensation layer 196 maycomprise one or more magnetic sublayers having the third invariablemagnetization direction 197.

The magnetic fixed layer 166 has a second invariable magnetizationdirection 167 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first invariablemagnetization direction 125. The magnetic fixed layer 166 may compriseone or more magnetic sublayers having the second invariablemagnetization direction 167.

The stacking order of the individual layers in the MTJ structure 229 ofthe memory element 228 may be inverted as illustrated in FIG. 14B. Thememory element 228′ of FIG. 14B has an MTJ structure 229′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 229. Accordingly, the magnetic compensation layer 196 and themagnetic fixed layer 166 may be formed adjacent to the optional seedlayer 118 and cap layer 120, respectively.

One or more of the magnetic layers 128, 130, 134, 136, 144, 154, 166,and 196 may comprise two, three, four, or more magnetic sublayers witheach magnetic sublayer being made of any suitable magnetic material,including magnetic metal, alloy, compound, or multilayer structure. Themagnetic sublayers of a magnetic layer may form adjacent to each otherand may have the same magnetization direction. For example, the magneticreference layer 144 of the embodiments of FIGS. 4A, 4B, 7A, 7B, 10A,10B, 13A, and 13B may further comprise three magnetic sublayers. FIGS.15A and 15B illustrate the magnetic reference layer 144 of theembodiments of FIGS. 7A and 7B comprising a first magnetic referencesublayer 234 formed adjacent to the insulating tunnel junction layer 126and a second magnetic reference sublayer 236 separated from the firstmagnetic reference sublayer 234 by an intermediate magnetic referencesublayer 266. Each of the first, second, and intermediate magneticreference sublayers 234, 236, and 266 may be made of any suitablemagnetic material or structure. The first, second, and intermediatemagnetic reference sublayers 234, 236, and 266 have the first invariablemagnetization direction 145 substantially perpendicular to the layerplanes thereof. Alternatively, the magnetic reference layer 144 of theembodiments of FIGS. 4A, 4B, 7A, 7B, 10A, 10B, 13A, and 13B may includetwo, four, or more magnetic sublayers, which may form adjacent to eachother and may have the same magnetization direction.

The second magnetic free layer 130 of the embodiments of FIGS. 3A, 3B,4A, 4B, 6A, 6B, 7A, 7B, 9A, 9B, 10A, 10B, 12A, 12B, 13A, and 13B mayfurther comprise a first magnetic free sublayer 280 formed adjacent tothe perpendicular enhancement layer (PEL) 132 and a second magnetic freesublayer 282 formed adjacent to the first magnetic free sublayer 280opposite the PEL 132 as illustrated in FIGS. 16A and 16B. Each of thefirst and second magnetic free sublayers 280 and 282 may be made of anysuitable magnetic material or structure as described above. The firstand second magnetic free sublayers 280 and 282 have the second variablemagnetization direction 131. Alternatively, the second magnetic freelayer 130 of the embodiments of FIGS. 3A, 3B, 4A, 4B, 6A, 6B, 7A, 7B,9A, 9B, 10A, 10B, 12A, 12B, 13A, and 13B may include three, four, ormore magnetic sublayers, which may form adjacent to each other and havethe same magnetization direction.

Similarly, the second magnetic reference layer 136 of the embodiments ofFIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, 11A, 11B, 12A, 12B, 14Aand 14B may further comprise a first magnetic reference sublayer 274formed adjacent to the perpendicular enhancement layer 138 and a secondmagnetic reference sublayer 276 separated from the first magneticreference sublayer 274 by an intermediate reference sublayer 278 asillustrated in FIGS. 17A and 17B. The first and second magneticreference sublayers 274 and 276 have the first invariable magnetizationdirection 125. The first and second magnetic reference sublayers 274 and276 each may be made of any suitable magnetic material or structure asdescribed above, such as but not limited to Co or CoFe, and may have athickness in the range of about 0.2 nm to about 1.2 nm. The intermediatereference sublayer 278 may be made of palladium, platinum, or nickel andmay have a thickness in the range of about 0.2 nm to about 1.2 nm.Alternatively, the second magnetic reference layer 136 of theembodiments of FIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, 11A, 11B,12A, 12B, 14A and 14B may include two or more magnetic sublayers, whichmay form adjacent to each other and have the same magnetizationdirection.

FIGS. 18A and 18B illustrate exemplary structures directed to theembodiments of FIGS. 6A, 6B, 8A, 8B, 12A, 12B, 14A, and 14B in which thesecond magnetic reference layer 136 comprises a first magnetic referencesublayer 290 formed adjacent to the PEL 138 and a second magneticreference sublayer 292 formed adjacent to the anti-ferromagneticcoupling layer 164. The first and second magnetic reference sublayers290 and 292 have the first invariable magnetization direction 125. Themagnetic fixed layer 166 in the exemplary structures of FIGS. 18A and18B may also comprise a second magnetic fixed sublayer 294 formedadjacent to the anti-ferromagnetic coupling layer 164 and a firstmagnetic fixed sublayer 296 formed adjacent to the second magnetic fixedsublayer 294. The first and second magnetic fixed sublayers 296 and 294have the second invariable magnetization direction 167 that issubstantially opposite to the first invariable magnetization direction125. One or more of the magnetic sublayers 290-296 may be made of anysuitable magnetic material or structure. At least one of the firstmagnetic reference sublayer 290, the second magnetic reference sublayer292, the first magnetic fixed sublayer 296, and the second magneticfixed sublayer 294 may have a multilayer structure, such as but notlimited to [Co/Pt], [Co/Pd], [Co/PtPd], [Co/Ni], [Co/Ir], [CoFe/Pt],[CoFe/Pd], [CoFe/PtPd], [CoFe/Ni], [CoFe/Ir], or any combinationthereof.

In addition to the examples described above, one or more of the magneticfree layer 154, the first magnetic free layer 128, the first magneticreference layer 134, and the magnetic compensation layer 196 may alsocomprise two, three, four, or more magnetic sublayers with each magneticsublayer being made of any suitable magnetic material, includingmagnetic metal, alloy, compound, or multilayer structure. The individualmagnetic sublayers of a magnetic layer may form adjacent to each otherand may have the same magnetization direction.

The magnetic fixed layer 166 of the embodiments of FIGS. 6A/B-8A/B,12A/B-15A/B, and 18A/B may include two or more magnetic sublayers with aperpendicular enhancement layer interposed therebetween. FIGS. 19A and19B illustrate exemplary structures directed to the embodiment of FIGS.8A and 8B in which the magnetic fixed layer 166 includes the secondmagnetic fixed sublayer 294 formed adjacent to the anti-ferromagneticcoupling layer 164 and the first magnetic fixed sublayer 296 separatedfrom the second magnetic fixed sublayer 294 by a perpendicularenhancement layer 298. The first and second magnetic fixed sublayers 296and 294 have the second invariable magnetization direction 167 that issubstantially perpendicular to layer planes thereof and is substantiallyopposite to the first invariable magnetization direction 125. One ormore of the magnetic fixed sublayers 294 and 296 may be made of anysuitable magnetic material or structure as described above. At least oneof the first and second magnetic fixed sublayers 294 and 296 may have amultilayer structure, such as but not limited to [Co/Pt], [Co/Pd],[Co/PtPd], [Co/Ni], [Co/Ir], [CoFe/Pt], [CoFe/Pd], [CoFe/PtPd],[CoFe/Ni], [CoFe/Ir], or any combination thereof.

Alternatively, the magnetic reference layer structure 124 of theexemplary structures of FIGS. 19A and 19B may include the first andsecond magnetic reference layers 134 and 136 without the perpendicularenhancement layer 138 in between, resulting in a thirteenth embodimentas illustrated in FIGS. 20A and 20B. A memory element 301 of FIG. 20Aincludes a magnetic tunnel junction (MTJ) structure 303 in between theoptional seed layer 118 and the optional cap layer 120. The MTJstructure 303 comprises the magnetic free layer 154, the insulatingtunnel junction layer 126 formed adjacent thereto, the first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 opposite the magnetic free layer 154, the second magneticreference layer 136 formed adjacent to the first magnetic referencelayer 134, the anti-ferromagnetic coupling layer 164 formed adjacent tothe second magnetic reference layer 136, and the magnetic fixed layer166 formed adjacent to the anti-ferromagnetic coupling layer 164. Themagnetic fixed layer 166 and the magnetic free layer 154 may be formedadjacent to the optional seed layer 118 and cap layer 120, respectively.Like the exemplary structures of FIGS. 19A and 19B, the magnetic fixedlayer 166 of the memory element 301 includes the second magnetic fixedsublayer 294 formed adjacent to the anti-ferromagnetic coupling layer164 and the first magnetic fixed sublayer 296 separated from the secondmagnetic fixed sublayer 294 by the perpendicular enhancement layer 298.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic free sublayers havingthe variable magnetization direction 155. The magnetic free layer 154and the magnetic sublayers thereof, if any, may be made of any suitablemagnetic material, including magnetic metal, alloy, compound, ormultilayer structure, as described above.

The first and second magnetic reference layers 134 and 136 have a firstinvariable magnetization direction 125 substantially perpendicular tothe layer planes thereof. Each of the first magnetic reference layer 134and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first invariable magnetization direction125. The first and second magnetic reference layers 134 and 136 and themagnetic sublayers thereof, if any, may be made of any suitable magneticmaterial, including magnetic metal, alloy, compound, or multilayerstructure.

The first and second magnetic fixed sublayers 296 and 294 have thesecond invariable magnetization direction 167 that is substantiallyperpendicular to the layer planes thereof and is substantially oppositeto the first invariable magnetization direction 125. One or more of themagnetic fixed sublayers 294 and 296 may be made of any suitablemagnetic material, including magnetic metal, alloy, compound, ormultilayer structure, as described above. At least one of the first andsecond magnetic fixed sublayers 294 and 296 may have a multilayerstructure, such as but not limited to [Co/Pt], [Co/Pd], [Co/PtPd],[Co/Ni], [Co/Ir], [CoFe/Pt], [CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ni],[CoFe/Ir], or any combination thereof.

The stacking order of the individual layers in the MTJ structure 303 ofthe memory element 301 may be inverted as illustrated in FIG. 20B. Thememory element 301′ of FIG. 20B has an MTJ structure 303′ that has thesame layers but with the inverted stacking order comparing to the MTJstructure 303. Accordingly, the magnetic free layer 154 and the magneticfixed layer 166 may be formed adjacent to the optional seed layer 118and cap layer 120, respectively.

The magnetic free layer structure 122 of the embodiments of FIGS. 3A/B,4A/B, 6A/B, 7A/B, 9A/B, 10A/B, 12A/B, 13A/B, 15A/B, and 16A/B mayinclude additional perpendicular enhancement layers (PELs) asillustrated in FIGS. 21A and 22A. The magnetic free layer structure 122shown in FIG. 21A includes a first magnetic free layer 128 formed on topof the insulating tunnel junction layer 126, a first PEL 132 formedadjacent to the first magnetic free layer 128 opposite the insulatingtunnel junction layer 126, a second magnetic free layer 130 formedadjacent to the first PEL 132 opposite the first magnetic free layer128, a second PEL 300 formed adjacent to the second magnetic free layer130 opposite the first PEL 132, and a third magnetic free layer 302formed adjacent to the second PEL 300 opposite the second magnetic freelayer 130. An optional cap layer (not shown) may form on top of thethird magnetic free layer 302. The first, second, and third magneticfree layers 128, 130, 302 have respectively the first, second, and thirdvariable magnetization directions 129, 131, 304 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129, and the second magnetic free layer130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. Likewise, the third magnetic freelayer 302 may comprise one or more magnetic sublayers having the thirdvariable magnetization direction 304. The first, second, and thirdvariable magnetization directions 129, 131, and 304 may be orientedparallel or anti-parallel to the variable magnetization directions ofadjacent layers. In an embodiment, all variable magnetization directions129, 131, and 304 have the same orientation (i.e., parallel to adjacentlayers). In another embodiment, the second variable magnetizationdirection 131 have an opposite orientation (anti-parallel) compared tothe first and third variable magnetization directions 129 and 304, whichhave the same orientation. For example and without limitation, theanti-ferromagnetic coupling between the first and second magnetic freelayers 128 and 130 in the above embodiment may be realized by using thefirst PEL 132 made of iridium. Similarly, the anti-ferromagneticcoupling between the second and third magnetic free layers 130 and 302may be realized by using the second PEL 300 made of iridium.

The stacking order of the individual layers in the magnetic free layerstructure 122 of FIG. 21A may be inverted as illustrated in FIG. 21B. Inthe inverted structure, the insulating tunnel junction layer 126 isformed on top of the first magnetic free layer 128.

FIG. 22A shows the magnetic free layer structure 122 incorporating threePELs. In addition to having the first, second, and third magnetic freelayers 128, 130, 302 and the first and second PELs 132, 300 like thestructure of FIG. 21A, the magnetic free layer structure 122 of FIG. 22Afurther includes a third PEL 306 formed adjacent to the third magneticfree layer 302 opposite the second PEL 300, and a fourth magnetic freelayer 308 formed adjacent to the third PEL 306 opposite the thirdmagnetic free layer 302. An optional cap layer (not shown) may form ontop of the fourth magnetic free layer 308. The first, second, third, andfourth magnetic free layers 128, 130, 302, 308 have respectively thefirst, second, third, and fourth variable magnetization directions 129,131, 304, 310 substantially perpendicular to the layer planes thereof.Analogous to the first, second, and third magnetic free layers 128, 130,302 described above, the fourth magnetic free layer 308 may comprise oneor more magnetic sublayers having the fourth variable magnetizationdirection 310. The first, second, third, and fourth variablemagnetization directions 129, 131, 304, and 310 may be oriented parallelor anti-parallel to the variable magnetization directions of adjacentlayers. In an embodiment, all variable magnetization directions 129,131, 304, and 310 have the same orientation (i.e., parallel to adjacentlayers). In another embodiment, all variable magnetization directions129, 131, 304, and 310 are oriented anti-parallel to the variablemagnetization directions of adjacent layers, which means that themagnetization directions 129 and 304 are oriented in a first directionwhile the magnetization directions 131 and 310 are oriented in a seconddirection substantially opposite to the first direction. For example andwithout limitation, the anti-ferromagnetic coupling between each of thefirst, second, third, and fourth magnetic free layers 128, 130, 302, 308and the adjacent magnetic layers in the above embodiment may be realizedby using the PELs 132, 300, 306 made of iridium.

The stacking order of the individual layers in the magnetic free layerstructure 122 of FIG. 22A may be inverted as illustrated in FIG. 22B. Inthe inverted structure, the insulating tunnel junction layer 126 isformed on top of the first magnetic free layer 128.

It is worth noting that the magnetic free layer structures 122 of FIGS.21A/B and 22A/B may have a body-centered cubic (BCC) lattice structure,especially when using CoFe or CoFeB alloy for one or more of themagnetic free layers 128, 130, 302, and 308. By contrast, theconventional multilayer structures, such as [Co/Pt] and [Co/Ni], formedby interleaving thin layers of magnetic material (i.e., cobalt) withthin layers of another material (i.e., platinum or nickel) may have aface-centered cubic (FCC) lattice structure or a superlattice structure,depending on the thicknesses of the individual layers.

FIGS. 23A/B show examples of the fourth embodiment (FIGS. 6A/B)incorporating the magnetic free layer structures 122 of FIGS. 22A/B. Thefirst, second, and third magnetic free layers 128, 130, and 302 may eachindependently include an magnetic alloy comprising cobalt and iron, suchas but not limited to CoFeB, CoFeTa, CoFeMo, CoFeMg, or CoFe. The firstand second PELs 132 and 300 of the magnetic free layer structure 122 mayeach independently include one of MgO or Mg. In an embodiment, the firstand second PELs 132 and 300 include Mg and MgO, respectively. Theinsulating tunnel junction layer 126 may include MgO. The first magneticreference layer 134 may include an magnetic alloy comprising cobalt andiron, such as but not limited to CoFeB, CoFeTa, CoFeMo, CoFeMg, or CoFe.The PEL 138 of the magnetic reference layer structure 124 may includeone of Mo, Ta, or W. The second magnetic reference layer 136 may includeCo or CoFe. The anti-ferromagnetic coupling layer 164 may include Ir.The magnetic fixed layer 166 may include layers of Co interleaved withlayers of Pt (i.e., [Co/Pt]) or layers of Ni (i.e., [Co/Ni]). Theoptional cap and seed layers 120 and 118 may include Mg0 and Cr,respectively.

The magnetic reference layer structure 124 of the embodiments of FIGS.3A/B, 5A/B, 6A/B, 8A/B, 9A/B, 11A/B, 12A/B, 14A/B, 17A/B, 18A/B, and19A/B may include additional perpendicular enhancement layers (PELs) asillustrated in FIGS. 24A and 25A. The magnetic reference layer structure124 shown in FIG. 24A includes a first magnetic reference layer 134formed beneath the insulating tunnel junction layer 126, a first PEL 138formed adjacent to the first magnetic reference layer 134 opposite theinsulating tunnel junction layer 126, a second magnetic reference layer136 formed adjacent to the first PEL 138 opposite the first magneticreference layer 134, a second PEL 312 formed adjacent to the secondmagnetic reference layer 136 opposite the first PEL 138, and a thirdmagnetic reference layer 314 formed adjacent to the second PEL 312opposite the second magnetic reference layer 136. The first, second, andthird magnetic reference layers 134, 136, and 314 each have the firstinvariable magnetization direction 125 substantially perpendicular tothe respective layer plane thereof. The first, second, and thirdmagnetic reference layers 134, 136, and 314 may each independentlyinclude one or more magnetic sublayers having the first invariablemagnetization direction 125.

The stacking order of the individual layers in the magnetic referencelayer structure 124 of FIG. 24A may be inverted as illustrated in FIG.24B. In the inverted structure, the first magnetic reference layer 134is formed on top of the insulating tunnel junction layer 126.

FIG. 25A shows the magnetic reference layer structure 124 incorporatingthree PELs. In addition to having the first, second, and third magneticreference layers 134, 136, and 314 and the first and second PELs 132 and300 like the structure of FIG. 24A, the magnetic reference layerstructure 124 of FIG. 25A further includes a third PEL 316 formedadjacent to the third magnetic reference layer 314 opposite the secondPEL 312, and a fourth magnetic reference layer 318 formed adjacent tothe third PEL 316 opposite the third magnetic reference layer 314. Thefirst, second, third, and fourth magnetic reference layers 134, 136,314, and 318 each have the first invariable magnetization direction 125substantially perpendicular to the respective layer plane thereof.Analogous to the first, second, and third magnetic reference layers 134,136, and 314 described above, the fourth magnetic reference layer 318may comprise one or more magnetic sublayers having the first invariablemagnetization direction 125.

The stacking order of the individual layers in the magnetic referencelayer structure 124 of FIG. 25A may be inverted as illustrated in FIG.25B. In the inverted structure, the first magnetic reference layer 134is formed on top of the insulating tunnel junction layer 126.

The magnetic free layers 128, 130, 154, 280, 282, 302, and 308, themagnetic reference layers 134, 136, 144, 234, 236, 266, 274-278, 290,292, 314, and 318, the magnetic fixed layer 166, 294 and 296, and themagnetic compensation layer 196 of above embodiments may be made of anysuitable magnetic material or structure. One or more of the magneticlayers 128, 130, 134, 136, 144, 154, 166, 196, 234, 236, 266, 274-282,290-296, 302, 308, 314, and 318 may each independently comprise at leastone ferromagnetic element, such as but not limited to cobalt (Co),nickel (Ni), or iron (Fe), to form a suitable magnetic material, such asbut not limited to Co, Ni, Fe, CoNi, CoFe, NiFe, or CoNiFe. The suitablemagnetic material for the one or more of the magnetic layers 128, 130,134, 136, 144, 154, 166, 196, 234, 236, 266, 274-282, 290-296, 302, 308,314, and 318 may further include one or more non-magnetic elements, suchas but not limited to boron (B), titanium (Ti), zirconium (Zr), hafnium(Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr),molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si), germanium(Ge), gallium (Ga), oxygen (O), nitrogen (N), carbon (C), platinum (Pt),palladium (Pd), ruthenium (Ru), samarium (Sm), neodymium (Nd), orphosphorus (P), to form a magnetic alloy or compound, such as but notlimited to cobalt-iron-boron (CoFeB), iron-platinum (FePt),cobalt-platinum (CoPt), cobalt-platinum-chromium (CoPtCr),cobalt-iron-boron-titanium (CoFeBTi), cobalt-iron-boron-zirconium,(CoFeBZr), cobalt-iron-boron-hafnium (CoFeBHf),cobalt-iron-boron-vanadium (CoFeBV), cobalt-iron-boron-tantalum(CoFeBTa), cobalt-iron-boron-chromium (CoFeBCr), cobalt-iron-titanium(CoFeTi), cobalt-iron-zirconium (CoFeZr), cobalt-iron-hafnium (CoFeHf),cobalt-iron-vanadium (CoFeV), cobalt-iron-niobium (CoFeNb),cobalt-iron-tantalum (CoFeTa), cobalt-iron-chromium (CoFeCr),cobalt-iron-molybdenum (CoFeMo), cobalt-iron-tungsten (CoFeW),cobalt-iron-aluminum (CoFeAl), cobalt-iron-silicon (CoFeSi),cobalt-iron-germanium (CoFeGe), iron-zirconium-boron (FeZrB),samarium-cobalt (SmCo), neodymium-iron-boron (NdFeB), orcobalt-iron-phosphorous (CoFeP).

Some of the above-mentioned magnetic materials, such as Fe, CoFe, CoFeBmay have a body-centered cubic (BCC) lattice structure that iscompatible with the halite-like cubic lattice structure of MgO, whichmay be used as the insulating tunnel junction layer 126. CoFeB alloyused for one or more of the magnetic layers 128, 130, 134, 136, 144,154, 166, 196, 234, 236, 266, 274-282, 290-296, 302, 308, 314, and 318may contain more than 40 atomic percent Fe or may contain less than 35atomic percent B or both.

The first magnetic reference layer 134 may be made of a magneticmaterial comprising Co, Fe, and B with a thickness in the range of about0.6 nm to about 1.8 nm, while the second magnetic reference layer 136may be made of elemental Co metal or an alloy comprising Co, Fe, and Bwith a thickness in the range of about 0.6 nm to about 2.0 nm.

One or more of the magnetic layers 128, 130, 134, 136, 144, 154, 166,196, 234, 236, 266, 274-282, 290-296, 302, 308, 314, and 318 mayalternatively have a multilayer structure formed by interleaving one ormore layers of a first type of material with one or more layers of asecond type of material with at least one of the two types of materialsbeing magnetic, such as but not limited to [Co/Pt], [Co/Pd], [Co/PtPd],[Co/Ni], [Co/Ir], [CoFe/Pt], [CoFe/Pd], [CoFe/PtPd], [CoFe/Ni],[CoFe/Ir], or any combination thereof. The multilayer structure may havea face-centered cubic (FCC) type of lattice structure, which isdifferent from the body-centered cubic structure (BCC) of someferromagnetic materials, such as Fe, CoFe, and CoFeB, and thehalite-like cubic lattice structure of magnesium oxide (MgO) that may beused as the insulating tunnel junction layer 126. All individualmagnetic layers of a magnetic multilayer structure may have the samemagnetization direction. The multilayer structure may or may not exhibitthe characteristic satellite peaks associated with superlattice whenanalyzed by X-ray, neutron diffraction, or other diffraction techniques.

The second magnetic free layer 130 of the embodiments of FIGS. 3A/B,4A/B, 6A/B, 7A/B, 9A/B, 10A/B, 12A/B, 13A/B, 15A/B, and 21A/B-23A/B maycomprise one or more ferromagnetic elements and may have a layerthickness of less than about 2 nm, preferably less than about 1.5 nm,more preferably less than about 1 nm, even more preferably less thanabout 0.8 nm, still even more preferably between about 0.7 nm and about0.1 nm. At a thickness of less than about 1.5 nm, the second magneticfree layer 130 may become superparamagnetic or magnetically dead byexhibiting no net magnetic moment in the absence of an external magneticfield. The second magnetic free layer 130 may have any suitablecomposition that comprises one or more of the following materials: Co,Ni, Fe, CoNi, CoFe, NiFe, CoNiFe, CoFeB, B, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Al, Si, Ge, Ga, O, N, C, Pt, Pd, Ru, Sm, Nd, and P.Alternatively, the second magnetic free layer 130 may have a nominalcomposition in which all ferromagnetic elements collectively account forless than about 80 at. %, preferably less than about 60 at. %, morepreferably less than about 50 at. %, even more preferably less thanabout 40 at. %. The second magnetic free layer 130 may becomenon-magnetic if the total content of the ferromagnetic elements is belowa certain threshold.

The insulating tunnel junction layer 126 for all perpendicular MTJstructures of FIGS. 3A/B-25A/B may be formed of a suitable insulatingmaterial containing oxygen, nitrogen, or both, such as but not limitedto magnesium oxide (MgO), aluminum oxide (AlO_(x)), titanium oxide(TiO_(x)), zirconium oxide (ZrO_(x)), hafnium oxide (HfO_(x)), vanadiumoxide (VO_(x)), tantalum oxide (TaO_(x)), chromium oxide (CrO_(x)),molybdenum oxide (MoO_(x)), tungsten oxide (WO_(x)), silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), or any combination thereof. Theinsulating tunnel junction layer 126 may have a halite-like cubiclattice structure.

The anti-ferromagnetic coupling layer 164, which anti-ferromagneticallycouples the magnetic fixed layer 166 to the magnetic reference layers136 and 144 in the MTJ structures of FIGS. 6A/B-8A/B, 12A/B-15A/B,18A/B-20A/B, and 23A/B, may have a single layer structure or maycomprise two, three, four, or more sublayers formed adjacent to eachother. One or more of the single layer and the multiple sublayers of theanti-ferromagnetic coupling layer 164 may each independently comprise asuitable anti-ferromagnetic coupling material, such as but not limitedto ruthenium (Ru), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), molybdenum (Mo), tungsten (W), manganese (Mn), rhenium (Re),osmium (Os), rhodium (Rh), iridium (Ir), copper (Cu), or any combinationthereof.

In embodiments where one or more of the magnetic fixed layer 166 and themagnetic reference layers 136 and 144 comprise a multilayer structure inwhich one of the two interleaving materials is non-magnetic, such as butnot limited to [Co/Pt], [Co/Pd], [Co/PtPd], [Co/Ir], [CoFe/Pt],[CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ir], an interface multilayer structurein which both of the two interleaving materials are magnetic, such asbut not limited to [Co/Ni] or [CoFe/Ni], may be inserted between themultilayer structure and the anti-ferromagnetic coupling layer 164,thereby improving the anti-ferromagnetic coupling between the magneticfixed layer 166 and the magnetic reference layers 136 and 144. Forexample, in the structures of FIGS. 18A/B, the first magnetic referencesublayer 290 and the first magnetic fixed sublayer 296 each may have amultilayer structure, such as but not limited to [Co/Pt], [Co/Pd],[Co/PtPd], [Co/Ir], [CoFe/Pt], [CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ir], orany combination thereof. Accordingly, the second magnetic referencesublayer 292 and the second magnetic fixed sublayer 294 each may have amultilayer structure in which both of the two interleaving materials aremagnetic, such as but not limited to [Co/Ni] or [CoFe/Ni], for improvingthe anti-ferromagnetic coupling between the magnetic fixed layer 166 andthe magnetic reference layer 136.

The perpendicular enhancement layers (PELs) 132, 138, 298, 300, 306,312, and 316 formed in the magnetic free layer structure 122, themagnetic reference layer structure 124, or the magnetic fixed layer 166may have a single layer structure or may comprise two, three, four, ormore perpendicular enhancement sublayers formed adjacent to each other.One or more of the single layer and the multiple sublayers of the PELs132, 138, 298, 300, 306, 312, and 316 may each independently have athickness less than about 3 nm, preferably less than about 2 nm, morepreferably less than about 1 nm, even more preferably less than about0.8 nm, still even more preferably less than about 0.6 nm. One or moreof the single layer and the multiple sublayers of the PELs 132, 138,298, 300, 306, 312, and 316 may each independently comprise one or moreof the following chemical elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al, Si,Ge, Ga, Be, Ba, Li, Ca, Sr, O, N, and C, thereby forming a suitableperpendicular enhancement material, such as but not limited to B, Mg,Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni,Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, MgO, TiO_(x), ZrO_(x), HfO_(x),VO_(x), NbO_(x), TaO_(x), CrO_(x), MoO_(x), WO_(x), RhO_(x), NiO_(x),PdO_(x), PtO_(x), CuO_(x), AgO_(x), RuO_(x), SiO_(x), TiN_(x), ZrN_(x),HfN_(x), VN_(x), NbN_(x), TaN_(x), CrN_(x), MoN_(x), WN_(x), NiN_(x),PdN_(x), PtO_(x), RuN_(x), SiN_(x), TiO_(x)N_(y), ZrO_(x)N_(y),HfO_(x)N_(y), VO_(x)N_(y), NbO_(x)N_(y), TaO_(x)N_(y), CrO_(x)M_(y),MoO_(x)N_(y), WO_(x)N_(y), NiO_(x)N_(y), PdO_(x)N_(y), PtO_(x)N_(y),RuO_(x)N_(y), SiO_(x)N_(y), TiRuO_(x), ZrRuO_(x), HfRuO_(x), VRuO_(x),NbRuO_(x), TaRuO_(x), CrRuO_(x), MoRuO_(x), WRuO_(x), RhRuO_(x),NiRuO_(x), PdRuO_(x), PtRuO_(x), CuRuO_(x), AgRuO_(x), CoFeB, CoFe,NiFe, CoFeNi, CoTi, CoZr, CoHf, CoV, CoNb, CoTa, CoFeTa, CoCr, CoMo,CoW, NiCr, NiTi, NiZr, NiHf, NiV, NiNb, NiTa, NiMo, NiW, CoNiTa, CoNiCr,CoNiTi, FeTi, FeZr, FeHf, FeV, FeNb, FeTa, FeCr, FeMo, FeW or anycombination thereof. In embodiments where the perpendicular enhancementmaterial contains one or more ferromagnetic elements, such as Co, Fe, orNi, the total content of the ferromagnetic elements of the perpendicularenhancement material may be less than the threshold required forbecoming magnetic, thereby rendering the material essentiallynon-magnetic. Alternatively, the perpendicular enhancement material thatcontains one or more ferromagnetic elements may be very thin, therebyrendering the material paramagnetic or magnetically dead. For example,the PEL 132, 138, 298, 300, 306, 312, and 316 may be made of a singlelayer of Ta, Hf, or MgO, or a bilayer structure with a Ta sublayer and aHf sublayer formed adjacent to each other.

The optional seed layer 118 of the embodiments of FIGS. 3AB-14A/B,19A/B-20A/B, and 23A/B may have a single layer structure or may comprisetwo, three, four, or more sublayers formed adjacent to each other. Oneor more of the single layer and the multiple sublayers of the seed layer118 may each independently have a thickness less than about 3 nm,preferably less than about 2 nm, more preferably less than about 1 nm,even more preferably less than about 0.8 nm, still even more preferablyless than about 0.6 nm. One or more of the single layer and the multiplesublayers of the seed layer 118 may each independently comprise one ormore of the following chemical elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta,Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al,Si, Ge, Ga, Be, Ba, Li, Ca, Sr, O, N, and C, thereby forming a suitableseed material such as one of those discussed above for the perpendicularenhancement material. For example, the seed layer 118 may comprise asingle layer of MgO, Ta, Hf, W, Mo, Ru, Pt, Pd, NiCr, NiTa, NiTi, orTaNx. Alternatively, the seed layer 118 may have a bilayer structurecomprising a Ta sublayer formed adjacent to one of the magnetic layers144, 154, 166, and 196 or structures 122 and 124 and a Ru sublayerformed beneath the Ta sublayer. Other exemplary bilayer structures(bottom/top), such as but not limited to Ir/Cr, CoFeB/Cr, Ta/Ru, Ta/Hf,Hf/Ta, Ta/W, W/Ta, Ru/W, W/Ru, MgO/Ta, Ta/MgO, Ru/MgO, Hf/MgO, andW/MgO, may also be used for the seed layer 118. Still alternatively, theseed layer 118 may have a bilayer structure comprising an oxidesublayer, such as MgO, formed adjacent to one of the magnetic layers144, 154, 166, and 196 or structures 122 and 124 and an underlying, thinconductive sublayer, such as CoFeB which may be non-magnetic oramorphous or both. Additional seed sublayers may further form beneaththe exemplary CoFeB/MgO seed layer to form other seed layer structures,such as but not limited to Ru/CoFeB/MgO, Ta/CoFeB/MgO, W/CoFeB/MgO,Hf/CoFeB/MgO, Ta/Ru/CoFeB/MgO, Ru/Ta/CoFeB/MgO, W/Ta/CoFeB/MgO,Ta/W/CoFeB/MgO, W/Ru/CoFeB/MgO, Ru/W/CoFeB/MgO, Hf/Ta/CoFeB/MgO,Ta/Hf/CoFeB/MgO, W/Hf/CoFeB/MgO, Hf/W/CoFeB/MgO, Hf/Ru/CoFeB/MgO,Ru/Hf/CoFeB/MgO, Ta/W/Ru/CoFeB/MgO, Ta/Ru/W/CoFeB/MgO, andRu/Ta/Ru/CoFeB/MgO. Still alternatively, the seed layer 118 may have amultilayer structure formed by interleaving seed sublayers of a firsttype with seed sublayers of a second type. One or both types of the seedsublayers may comprise one or more ferromagnetic elements, such as Co,Fe, or Ni. One or both types of seed sublayers may be amorphous ornoncrystalline. For example, the first and second types of sublayers maybe made of Ta and CoFeB, both of which may be amorphous. Moreover, oneof the Ta sublayers may be formed adjacent to one of the magnetic layers144, 154, 166, and 196 or structures 122 and 124 and the CoFeB sublayersmay be non-magnetic or superparamagnetic.

The optional cap layer 120 of the embodiments of FIGS. 3AB-14A/B, 19A/B,20A/B, and 23A/B may have a single layer structure or may comprise two,three, four, or more sublayers formed adjacent to each other. One ormore of the single layer and the multiple sublayers of the cap layer 120may each independently have a thickness less than about 3 nm, preferablyless than about 2 nm, more preferably less than about 1 nm, even morepreferably less than about 0.8 nm, still even more preferably less thanabout 0.6 nm. One or more of the single layer and the multiple sublayersof the cap layer 120 may each independently comprise one or more of thefollowing chemical elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W,Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga,Be, Ba, Li, Ca, Sr, O, N, and C, thereby forming a suitable cap materialsuch as one of those discussed above for the perpendicular enhancementmaterial. For example, the cap layer 120 may comprise a single layer ofMgO, Ta, Hf, W, Mo, Ru, Pt, or Pd. Alternatively, the cap layer 120 mayhave a bilayer structure comprising a W sublayer formed adjacent to oneof the magnetic layers 144, 154, 166, and 196 or structures 122 and 124and a Ta sublayer formed on top of the W sublayer. Other exemplarybilayer structures (bottom/top), such as but not limited to Ta/Ru,Ru/Ta, Ta/Hf, Hf/Ta, Ta/W, Ru/W, W/Ru, MgO/Ta, Ta/MgO, MgO/Ru, MgO/Hf,and MgO/W, may also be used for the cap layer 120. Still alternatively,the cap layer 120 may have a bilayer structure comprising an oxidesublayer, such as but not limited to MgO, formed adjacent to one of themagnetic layers 144, 154, 166, and 196 or structures 122 and 124 and athin conductive sublayer, such as CoFeB, which may be non-magnetic orsuperparamagnetic, formed on top of the MgO sublayer. Additional capsublayers may further form on top of the exemplary MgO/CoFeB cap layerto form other cap layer structures, such as but not limited toMgO/CoFeB/Ru, MgO/CoFeB/Ta, MgO/CoFeB/W, MgO/CoFeB/Hf, MgO/CoFeB/Ru/Ta,MgO/CoFeB/Ta/Ru, MgO/CoFeB/W/Ta, MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ru,MgO/CoFeB/Ru/W, MgO/CoFeB/Hf/Ta, MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W,MgO/CoFeB/W/Hf, MgO/CoFeB/Hf/Ru, MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ru/W/Ta,MgO/CoFeB/W/Ru/Ta, and MgO/CoFeB/Ru/Ta/Ru. As such, the cap layer 120may comprise an insulating cap sublayer and one or more conductive capsublayers formed thereon.

The tuning layer 194 of the embodiments of FIGS. 9A/B-14A/B may have asingle layer structure or may comprise two, three, four, or moresublayers formed adjacent to each other. One or more of the single layerand the multiple sublayers of the tuning layer 194 may eachindependently have a thickness less than about 3 nm, preferably lessthan about 2 nm, more preferably less than about 1 nm, even morepreferably less than about 0.8 nm, still even more preferably less thanabout 0.6 nm. One or more of the single layer and the multiple sublayersof the tuning layer 194 may each independently comprise one or more ofthe following chemical elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al, Si, Ge,Ga, Be, Ba, Li, Ca, Sr, O, N, and C, thereby forming a suitable tuningmaterial such as one of those discussed above for the perpendicularenhancement material. For example, the tuning layer 194 may comprise asingle layer of MgO, Ta, Hf, W, Mo, Pt, or Pd. Alternatively, the tuninglayer 194 may have a bilayer structure comprising a W sublayer formedadjacent to the magnetic free layer 154 or structure 122 and a Tasublayer formed adjacent to the compensation layer 196. Other exemplarybilayer structures, such as but not limited to Ta/Ru, Ru/Ta, Ta/Hf,Hf/Ta, Ta/W, Ru/W, W/Ru, MgO/Ta, Ta/MgO, MgO/Ru, MgO/Hf, and MgO/W withthe first of the two materials being disposed adjacent to the magneticfree layer 154 or 130, may also be used for the tuning layer 194. Stillalternatively, the tuning layer 194 may have a bilayer structurecomprising an oxide sublayer, such as but not limited to MgO, formedadjacent to the magnetic free layer 154 or 130 and a thin conductivesublayer, such as but not limited to CoFeB which may be non-magnetic orsuperparamagnetic. Additional tuning sublayers may further form adjacentto the exemplary MgO/CoFeB tuning layer to form other tuning layerstructures, such as but not limited to MgO/CoFeB/Ru, MgO/CoFeB/Ta,MgO/CoFeB/W, MgO/CoFeB/Hf, MgO/CoFeB/Ru/Ta, MgO/CoFeB/Ta/Ru,MgO/CoFeB/W/Ta, MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ru, MgO/CoFeB/Ru/W,MgO/CoFeB/Hf/Ta, MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W, MgO/CoFeB/W/Hf,MgO/CoFeB/Hf/Ru, MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ru/W/Ta, MgO/CoFeB/W/Ru/Ta,and MgO/CoFeB/Ru/Ta/Ru. As such, the tuning layer 194 may comprise aninsulating tuning sublayer formed adjacent to the magnetic free layer130 or 154 and one or more conductive tuning sublayers formed adjacentto the insulating tuning sublayer.

It should be noted that the MTJ memory element of the present inventionmay be used in any suitable memory device, not just the conventionalmemory device illustrated in FIG. 1. For example, the MTJ memory elementof the present invention may be used in a novel memory device disclosedin U.S. Pat. No. 8,879,306 in which each MTJ memory element is coupledto two transistors.

The previously described embodiments of the present invention have manyadvantages, including high perpendicular anisotropy, minimum offsetfield, and improved anti-ferromagnetic coupling. It is important tonote, however, that the invention does not require that all theadvantageous features and all the advantages need to be incorporatedinto every embodiment of the present invention.

While the present invention has been shown and described with referenceto certain preferred embodiments, it is to be understood that thoseskilled in the art will no doubt devise certain alterations andmodifications thereto which nevertheless include the true spirit andscope of the present invention. Thus the scope of the invention shouldbe determined by the appended claims and their legal equivalents, ratherthan by examples given.

What is claimed is:
 1. A magnetic memory element comprising: a magneticfree layer structure including: first and second magnetic free layershaving a variable magnetization direction substantially perpendicular tolayer planes thereof, said first and second magnetic free layers eachcomprising cobalt and iron; and a first perpendicular enhancement layer(PEL) interposed between said first and second magnetic free layers; aninsulating tunnel junction layer formed adjacent to said first magneticfree layer opposite said first PEL; a magnetic reference layer structureincluding: first, second, and third magnetic reference layers having afirst invariable magnetization direction substantially perpendicular tolayer planes thereof, said first magnetic reference layer comprisingcobalt and iron and formed adjacent to said insulating tunnel junctionlayer opposite said first magnetic free layer; a second PEL interposedbetween said first and second magnetic reference layers and comprisingany one of magnesium, tantalum, molybdenum, or tungsten; and a third PELinterposed between said second and third magnetic reference layers andcomprising any one of magnesium, tantalum, molybdenum, or tungsten; ananti-ferromagnetic coupling layer formed adjacent to said third magneticreference layer opposite said third PEL; and a magnetic fixed layerformed adjacent to said anti-ferromagnetic coupling layer opposite saidthird magnetic reference layer, said magnetic fixed layer having asecond invariable magnetization direction substantially opposite to saidfirst invariable magnetization direction.
 2. The magnetic memory elementaccording to claim 1, wherein said magnetic free layer structure isdeposited on top of said insulating tunnel junction layer.
 3. Themagnetic memory element according to claim 1, wherein said first andsecond magnetic free layers have a body-centered cubic latticestructure.
 4. The magnetic memory element according to claim 1, whereinsaid first and second magnetic free layers each further comprise boron.5. The magnetic memory element according to claim 1, wherein said firstPEL comprises any one of magnesium, tantalum, molybdenum, or tungsten.6. The magnetic memory element according to claim 5, wherein said firstPEL further comprises oxygen.
 7. The magnetic memory element accordingto claim 1, wherein said first PEL comprises any one of titanium,zirconium, vanadium, or aluminum.
 8. The magnetic memory elementaccording to claim 1, wherein said magnetic free layer structure furthercomprises a third magnetic free layer and a fourth PEL interposedbetween said second and third magnetic free layer.
 9. The magneticmemory element according to claim 8, wherein said third magnetic freelayer comprises cobalt and iron.
 10. The magnetic memory elementaccording to claim 8, wherein said fourth PEL comprises any one ofmagnesium, tantalum, molybdenum, or tungsten.
 11. The magnetic memoryelement according to claim 1, wherein said first magnetic referencelayer further comprises boron.
 12. The magnetic memory element accordingto claim 1, wherein said second magnetic reference layer comprisescobalt and iron.
 13. The magnetic memory element according to claim 1,wherein said third magnetic reference layer comprises cobalt.
 14. Themagnetic memory element according to claim 1, wherein said second PELfurther comprises oxygen.
 15. The magnetic memory element according toclaim 1, wherein said second PEL further comprises cobalt and iron. 16.The magnetic memory element according to claim 1, wherein said third PELfurther comprises oxygen.
 17. The magnetic memory element according toclaim 1, wherein said third PEL further comprises cobalt and iron. 18.The magnetic memory element according to claim 1 further comprising amagnesium oxide cap layer formed adjacent to said second magnetic freelayer.
 19. The magnetic memory element according to claim 1, whereinsaid anti-ferromagnetic coupling layer comprises any one of iridium orruthenium.
 20. The magnetic memory element according to claim 1, whereinsaid magnetic fixed layer has a multilayer structure comprising layersof cobalt interleaved with layers of platinum.